Long-term wear of HIPed alumina on alumina bearings for THR under microseparation conditions.

The long term wear and wear debris generated in HIPed alumina on alumina bearings for hip prostheses with microseparation in vitro is compared to standard simulator conditions and ex vivo specimens. Microseparation studies were completed to five million cycles at two severity levels in attempts to rigorously evaluate the long-term tribological performance of the bearings. During the first million cycles (bedding-in) of the microseparation tests characteristic stripe wear was observed on all of the femoral heads with a matching area on the rim of the acetabular inserts. Under mild microseparation conditions an average wear rate of 0.55 mm3/million cycles was observed during the initial million cycles which reduced to a steady state level of 0.1 mm3/million cycles. Under more severe conditions an average wear rate of 4.0 mm3/million cycles was observed during bedding-in which reduced to a steady state level of 1.3 mm3/million cycles. These compare to a bedding-in wear rate of 0.11 mm3/million cycles and steady-state wear rate of 0.05 mm3/million cycles for the same material under normal simulation with no microseparation. Furthermore, under microseparation the wear mechanisms and wear debris were similar to those observed in previous alumina retrieval studies with debris ranging from 10 nm to 1 microm in size.